1. Field of the Invention
The present invention relates to a test apparatus for phonograph pickup needles and styli for determining the amount of wear of the scanning point of the styli.
2. Brief Description of the Background of the Invention Including Prior Art
Conventional test equipment of the kind set forth above usually comprises essentially a microscope, a special support provision for a reproducing needle, and an illumination provision. The magnification has to be such that the length of the ground-off surface of the point of the needle of for examaple 5 to 8 micrometers can be easily recognized, since an elliptically ground needle follows the flanks of the grooves because of the short wavelengths of about 15 micrometer for example with a radius of only 5 to 8 micrometer.
Therefore, such test equipment is expensive and not suitable for the general consumer. Because of the relatively high price frequently insufficient microscopes, in particular with respect to the magnification, are employed and thus the determination of the degree of wear becomes indefinite. In addition to the existing technical problems there is further present in many cases a lack of confidence between the customer and the shop or, respectively, the seller of the needle.
In view of this, simple provisions for the general consumer to determine the wear of a needle are already known. These provisions determine the wear in an indirect way by measuring the playing time (German Patent Application Laid Out DE-AS No. 1,091,359 and British Patent Specification No. 2,045,994). In fact, these provisions are substantially cheaper and can also be manipulated easily by the general consumer, but they are associated with the disadvantage that they lead to very inaccurate results. For example, the size of the rounding radius can be taken summarily from a table for correction purposes of the playing time in case of sapphire or diamond, but this is no longer in general possible because of the considerable hardness differences, which can for example amount to a ratio of 1:5 in the case of diamond depending on the disposition of the crystal axes. The same holds true for differing wear hardnesses of phonorecords. In addition, the determination of the actual scanning path length, over which the needle passes, proves to be difficult (German Patent Application Laid Out Nos. 1,200,009 and 1,211,416).